Powder paint and painted article

ABSTRACT

To provide a powder paint whereby an external defect such as orange-peel skin is less likely to be formed on a formed cured film. The powder paint is characterized by comprising: a fluororesin (A); from 2 to 60 mass ppm relative to the fluororesin (A), of at least one metal element (B) selected from a group comprising potassium, sodium, and magnesium; from 10 to 10,000 mass ppm relative to the fluororesin (A), of a light stabilizer (C); and from 10 to 5,000 mass ppm relative to the fluororesin (A), of a polymerization inhibitor (D).

This application is a continuation of PCT Application No.PCT/JP2015/061495, filed on Apr. 14, 2015, which is based upon andclaims the benefit of priority from Japanese Patent Application No.2014-086256 filed on Apr. 18, 2014. The contents of those applicationsare incorporated herein by reference in their entireties.

TECHNICAL FIELD

The present invention relates to a powder paint and a painted article.

BACKGROUND ART

In recent years, environmental pollution of global scale, such as globalwarming, ozone layer depletion, acid rain, is an international problem.For this reason, it has become an urgent need to establish measuresagainst environmental pollution, and currently, various emissionregulations are being carried out in each country from the point of viewof environmental protection. Among them, since the problem of dischargeinto the atmosphere of organic solvents (VOC) is critical, reduction oforganic solvents (de-VOC) is underway under enhanced VOCemission-control regulations, particularly in the paint industry.

Heretofore, VOC have been used for paints, but as de-VOC has beenpromoted, more recently, it has become common to widely use powderpaints presenting little environmental impact, which contain no VOC atall and thus require no exhaust treatment or wastewater treatment andwhich can further be recovered and reused.

Previously, as raw materials for powder paints, acrylic resins,polyester resins or epoxy resins have been primarily used.

However, cured films formed by the powder paints containing them as rawmaterials, are not sufficient in weather resistance.

Under the circumstances, attention has been drawn to a fluororesin as aresin which can be used for a powder paint and is excellent in weatherresistance.

As a powder paint composition containing a fluororesin, for example, apowder coating composition comprising a hydroxy group-containingfluororesin and a polyuretdione curing agent or a blocked isocyanatecuring agent may be mentioned (Patent Document 1).

PRIOR ART DOCUMENT Patent Document

Patent Document 1: JP-A-2003-105269

DISCLOSURE OF INVENTION Technical Problem

However, if melt-kneading or the like is conducted by using a powderpaint composition disclosed in Patent Document 1, the molecular weightof the hydroxy group-containing fluororesin tends to increase during themelt-kneading, and on a cured film to be formed from such a composition,abnormal appearance such as orange peel is likely to be formed.

It is an object of the present invention, to provide a powder paintcapable of forming a cured film having excellent surface quality bypreventing abnormal appearance such orange peel.

Solution to Problem

The present invention provides a powder paint and a painted articlehaving the following constructions [1] to [13].

[1] A powder paint characterized by comprising

a fluororesin (A),

from 2 to 60 mass ppm relative to the fluororesin (A), of at least onemetal element (B) selected from the group consisting of potassium,sodium and magnesium,

from 10 to 10,000 mass ppm relative to the fluororesin (A), of a lightstabilizer (C) and,

from 10 to 5,000 mass ppm relative to the fluororesin (A), of apolymerization inhibitor (D).

[2] The powder paint according to the above [1], wherein the fluororesin(A) is at least one member selected from the group consisting of apolyvinylidene fluoride and a copolymer containing units based on afluoroolefin and units having a reactive group.

[3] The powder paint according to the above [1] or [2], wherein thefluororesin (A) is a fluororesin having a glass transition temperatureof at least 30° C.

[4] The powder paint according to any one of the above [1] to [3],wherein the fluororesin (A) has a number average molecular weight offrom 3,000 to 50,000.

[5] The powder paint according to any one of the above [1] to [4], whichfurther contains from 0.1 to 30 mass ppm relative to the fluororesin(A), of free chlorine atoms.

[6] The powder paint according to the above [5], wherein the mass ratioof the metal element (B) to the free chlorine atoms is from 1.0 to 10.0.

[7] The powder paint according to any one of the above [1] to [6], whichfurther contains from 10 to 400 parts by mass of a non-fluororesin (E)per 100 parts by mass of the fluororesin (A).

[8] The powder paint according to any one of the above [1] to [7],wherein the light stabilizer (C) is a hindered amine light stabilizerhaving a molecular weight of from 300 to 5,000 and a melting point offrom 50 to 250° C.

[9] The powder paint according to any one of the above [1] to [8],wherein the polymerization inhibitor (D) is a hydroquinone.

[10] The powder paint according to any one of the above [7] to [9],wherein the non-fluororesin (E) is an acrylic resin or a polyesterresin.

[11] A painted article having a cured film of the powder paint asdefined in any one of the above [1] to [10] on the surface of asubstrate.

[12] The painted article according to the above [11], wherein thethickness of the cured film is from 100 to 1,000 μm.

[13] The painted article according to the above [11] or [12], whereinthe water contact angle of the cured film is from 1 to 55°.

Advantageous Effects of Invention

According to the powder paint of the present invention, it is possibleto prevent an increase in the molecular weight of the fluororesin duringthe production of the powder paint; a cured film to be formed will havean excellent surface quality; and it is possible to prevent abnormalappearance such as orange peel.

DESCRIPTION OF EMBODIMENTS

The following definitions of terms are applicable throughout thespecification including Claims.

A “glass transition temperature” means the mid-point glass transitiontemperature measured by a differential scanning calorimetry (DSC)method.

A “fluororesin” means a polymer compound having fluorine atoms in themolecule.

A “non-fluororesin” means a polymer compound having no fluorine atom inthe molecule.

A “cured film” means a film formed by applying and curing a powderpaint.

A “(meth) acrylate” is a generic term for an acrylate and methacrylate.

A “unit” is a moiety based on a monomer constituting the structure of apolymer, and refers to a structural unit formed by polymerization of themonomer or a structural unit obtained by chemically converting such astructural unit. For example, in a case where a polymer is one to beformed by addition polymerization of a monomer having a carbon-carbonunsaturated double bond, a unit of the polymer is a divalent unit formedby cleavage of the carbon-carbon unsaturated double bond of the monomerby the polymerization reaction.

[Powder Paint]

The powder paint of the present invention is characterized by comprisingthe fluororesin (A), at least one metal element (B) selected from thegroup consisting of potassium, sodium and magnesium, a light stabilizer(C) and a polymerization inhibitor (D) and, as the case requires, anon-fluororesin (F), additives, etc.

(Fluororesin (A))

The fluororesin (A) may, for example, be a homopolymer or copolymerhaving units based on a fluoroolefin.

The fluoroolefin is a compound having at least one hydrogen atom in ahydrocarbon olefin (general formula C_(n)H_(2n)) substituted by afluorine atom.

The number n of carbon atoms in the fluoroolefin is preferably from 2 to8, particularly preferably from 2 to 6.

The number of fluorine atoms in the fluoroolefin is preferably at least2, particularly preferably 3 or 4. When the number of fluorine atoms isat least 2, the cured film will be excellent in weather resistance.

In the fluoroolefin, at least one hydrogen atom not substituted by afluorine atom may be substituted by a chlorine atom. When thefluoroolefin has chlorine atom(s), it becomes easy to disperse a pigment(especially a colored organic pigment such as cyanine blue or cyaninegreen), etc. in the fluororesin (A). Further, the glass transitiontemperature of the fluororesin (A) can be designed to be at least 30°C., and blocking of a cured film can be suppressed.

As the fluoroolefin, at least one member selected from the groupconsisting of tetrafluoroethylene (hereinafter referred to as “TFE”),chlorotrifluoroethylene (hereinafter referred to as “CTFE”),hexafluoropropylene and vinyl fluoride is preferred, and TFE or CTFE isparticularly preferred.

One of such fluoroolefins may be used alone or two or more of them maybe used in combination.

When the fluororesin (A) is a homopolymer having units based on afluoroolefin, it may, for example, be polyvinylidene fluoride(hereinafter referred to as “PVDF”), polyvinyl fluoride,polychlorotrifluoride, etc., and PVDF is particularly preferred in thatit is excellent in adhesion to a substrate (especially to an aluminumsubstrate), and it can easily be fixed on an aluminum curtain wall witha sealing agent.

When the fluororesin (A) is a copolymer having units based on afluoroolefin, it is preferably a copolymer having units based on afluoroolefin and units having a reactive group, in that it is excellentin antifouling property, water resistance, acid resistance, alkaliresistance, etc. Further, it may have other units (hereinafter referredto as “other units”) in addition to units based on a fluoroolefin andunits having a reactive group.

The units having a reactive group, may be units obtained by polymerizinga monomer having a reactive group, or units having some or all of unitschemically convertible to form reactive groups, in a copolymer,chemically converted to form reactive groups. The units having areactive group may be of one type, or of two or more types.

The reactive group may, for example, be a hydroxy group, a carboxygroup, an amino group. etc. Among them, a hydroxy group or a carboxygroup is preferred as the reactive group, since in the case of using anisocyanate-type curing agent (especially a blocked isocyanate-typecuring agent) as the curing agent, the curing speed will be excellent,it becomes easy to disperse a pigment, etc., and it is possible toobtain a cured film with a high gloss (60° gloss being at least 60%).

A unit having a hydroxy group may be a unit obtained by polymerizing amonomer having a hydroxy group. For example, allyl alcohol, ahydroxyalkyl vinyl ether (2-hydroxyethyl vinyl ether, 4-hydroxybutylvinyl ether, cyclohexanediol monovinyl ether, etc.), a hydroxyalkylallyl ether (2-hydroxyethyl allyl ether, etc.), a vinyl hydroxyalkanoate (vinyl hydroxypropionate, etc.), a hydroxyalkyl (meth)acrylate(hydroxyethyl (meth)acrylate, etc.), etc. may be mentioned.

A unit having a carboxy group may, for example, be a unit obtained bypolymerizing a monomer having a carboxy group, or a unit having acarboxyl group that is formed by chemical conversion. For example,(meth)acrylic acid, a carboxyl alkyl vinyl ether, carboxyl allyl ether,etc. may be mentioned.

As a method of forming a unit having a carboxy group by a chemicalconversion, preferred is a method of copolymerizing the above monomerhaving a hydroxy group to form a unit having a hydroxy group, followedby an esterification reaction of an acid anhydride to the hydroxy groupto obtain a unit having a carboxy group.

The acid anhydride is preferably a compound having a molecular weight offrom 90 to 200, preferably a compound having from 4 to 15 carbon atoms,preferably a compound having a melting point of from 20 to 180° C., fromthe viewpoint of excellent reactivity with the hydroxyl group.

The acid anhydride may be a dibasic acid anhydride. For example,succinic anhydride (molecular weight: 100.1, melting point: 120° C., thenumber of carbon atoms: 4), glutaric anhydride (molecular weight: 114.1,melting point: 52° C., the number of carbon atoms: 5), itaconicanhydride (molecular weight: 112.1, melting point: 67° C., the number ofcarbon atoms: 5), anhydrous 1,2-cyclohexane dicarboxylic acid(hexahydrophthalic anhydride) (molecular weight: 154.0, melting point:35° C., the number of carbon atoms: 8), anhydrouscis-4-cyclohexene-1,2-dicarboxylic acid (molecular weight: 152.0,melting point: 66° C., the number of carbon atoms: 8), phthalicanhydride (molecular weight: 148.1, melting point: 131° C., the numberof carbon atoms: 8), 4-methylhexahydrophthalic anhydride (molecularweight: 168.0, melting point: 22° C., the number of carbon atoms: 9),anhydrous 1,8-naphthalic acid (molecular weight: 198.2, melting point:17° C., the number of carbon atoms: 11), maleic anhydride (molecularweight: 98.1, melting point: 52.6° C., the number of carbon atoms: 4),etc. may be mentioned.

As the dibasic acid anhydride, succinic anhydride is particularlypreferred from the viewpoint of the solubility and reactivity with ahydroxyl group.

Other units may, for example, be units based on a fluorinated monomerother than a fluoroolefin, or units based on other monomers having nofluorine atom and no reactive group (hereinafter referred to as “othermonomers”).

The fluorinated monomer other than a fluoroolefin may, for example, be afluoro(alkyl vinyl ether), etc.

Other monomers are preferably vinyl-type monomers, since they areexcellent in alternating copolymerizability with a fluoroolefin, and itis possible to increase the polymerization yield.

Further, the vinyl-type monomers are preferred, since even when remainedas unreacted, they present little influence on the cured film, and theycan easily be removed in the production process.

As such vinyl monomers, for example, vinyl ethers, allyl ethers, alkylvinyl esters, alkyl allyl esters, olefins, etc. may be mentioned.

The vinyl ethers may, for example, be cycloalkyl vinyl ethers (such ascyclohexyl vinyl ether (hereinafter referred to as “CHVE”.), etc.),alkyl vinyl ethers (such as nonyl vinyl ether, 2-ethylhexyl vinyl ether,hexyl vinyl ether, ethyl vinyl ether, n-butyl vinyl ether, tert-butylvinyl ether, etc.), etc.

The allyl ethers may, for example, be alkyl allyl ethers (such as ethylallyl ether, hexyl allyl ether, etc.).

The alkyl vinyl esters may, for example, be vinyl esters of carboxylicacids (such as acetic acid, butyric acid, pivalic acid, benzoic acid,propionic acid, etc.). Also, as a vinyl ester of a carboxylic acidhaving a branched alkyl group, commercially available VeoVa-9, VeoVa-10(both manufactured by Shell Chemical Co., trade names), etc. may beused.

The alkyl allyl esters may, for example, be allyl esters of carboxylicacids (such as acetic acid, butyric acid, pivalic acid, benzoic acid,propionic acid, etc.).

The olefins may, for example, be ethylene, propylene, isobutylene, etc.

As other units, units based on a cycloalkyl vinyl ether are preferred,and units based on CHVE are particularly preferred, whereby the glasstransition temperature of the fluororesin (A) can be designed to be atleast 30° C., and it is possible to suppress blocking of the cured film.

As other units, preferred are units having a linear or branched alkylgroup having 3 or more carbon atoms from the viewpoint of excellentflexibility of the cured film.

As other units, one type may be used alone, or two or more types may beused in combination.

The fluororesin (A) may, for example, be a TFE-perfluoro(alkyl vinylether) copolymer (hereinafter referred to as “PFA”), aTFE-hexafluoropropylene copolymer, a TFE-perfluoro(alkyl vinylether)-hexafluoropropylene copolymer, an ethylene-TFE copolymer(hereinafter referred to as “ETFE”), an ethylene-CTFE copolymer, etc.

Among them, as a combination of monomers forming the units constitutingthe fluororesin (A), the following combination (1) is preferred,combination (2) is more preferred, and combination (3) is particularlypreferred, from the viewpoint of weather resistance, adhesion,flexibility, blocking resistance, etc.

Combination (1)

Fluoroolefin: TFE or CTFE,

Monomer having a hydroxy group: hydroxyalkyl vinyl ether,

Other monomers: at least one member selected from a cycloalkyl vinylether, an alkyl vinyl ether and an alkyl vinyl ester.

Combination (2)

Fluoroolefin: TFE or CTFE,

Monomer having a hydroxy group: hydroxyalkyl vinyl ether,

Other monomers: CHVE or tert-butyl ether.

Combination (3)

Fluoroolefin: CTFE,

Monomer having a hydroxy group: hydroxyalkyl vinyl ether,

Other monomers: CHVE or tert-butyl ether.

The proportion of units based on a fluoroolefin, is preferably from 30to 70 mol %, particularly preferably from 40 to 60 mol %, in all units(100 mol %) in the copolymer. When the proportion of the units based ona fluoroolefin is at least the above lower limit value, the cured filmwill be excellent in weather resistance. When the proportion of theunits based on a fluoroolefin is at most the above upper limit value, ina case where the cured film has a single layer structure, it will beexcellent in adhesion between the layer and the substrate, and in a casewhere the cured film has a two-layer structure, it will be excellent inadhesion between a layer formed by the fluororesin (A) and a layerformed by the non-fluororesin (E).

The proportion of units having a reactive group is preferably from 0.5to 20 mol %, particularly preferably from 1 to 15 mol %, in all units(100 mol %) in the copolymer. When the proportion of the units having areactive group is at least the above lower limit value, in a case wherethe cured film has a single layer structure, it will be excellent inadhesion between the layer and the substrate, and in a case where thecured film has a two-layer structure, it will be excellent in adhesionbetween a layer formed by the fluororesin (A) and a layer formed by thenon-fluororesin (E). When the proportion of the units having a reactivegroup is at most the above upper limit value, scratch resistance of thecured film will be excellent.

The proportion of other units is preferably from 20 to 60 mol %,particularly preferably from 30 to 50 mol %, in all units (100 mol %) inthe copolymer. When the proportion of other units is at least the abovelower limit value, the glass transition temperature of the fluororesin(A) can be set in an appropriate range, and it is easy to produce apowder paint. When the proportion of other units is at most the aboveupper limit value, in a case where the cured film has a single layerstructure, it will be excellent in adhesion between the layer and thesubstrate, and in a case where the cured film has a two-layer structure,it will be excellent in adhesion between a layer formed by thefluororesin (A) and a layer formed by the non-fluororesin (E).

The proportions of these units substantially coincide with the chargedamounts at the time of polymerization.

The melting point of the fluororesin (A) is preferably at most 300° C.,more preferably at most 200° C., particularly preferably at most 180° C.When the melting point of the fluororesin (A) is at most the above upperlimit value, the surface smoothness of the cured film will be furtherexcellent. Usually, the melting point is at least 35° C.

The lower limit of the glass transition temperature of the fluororesin(A) is preferably at least 30° C., particularly preferably at least 35°C., whereby it will be easy to produce a powder paint, and it will beeasy to prevent blocking.

On the other hand, the upper limit of the glass transition temperatureof the fluororesin (A), is preferably at most 150° C., more preferablyat most 120° C., particularly preferably at most 100° C., from such aviewpoint that it is possible to further improve the surface smoothnessof the formed cured film.

The number average molecular weight of the fluororesin (A) is preferablyfrom 3,000 to 50,000, particularly preferably from 5,000 to 30,000. Whenthe number average molecular weight is at least the above lower limitvalue, the cured film will be excellent in water resistance, salt waterresistance, etc. When the number average molecular weight is at most theupper limit value, the surface smoothness of the cured film will be moreexcellent.

In a case where the fluororesin (A) has reactive groups such as hydroxygroups whereby it is possible to measure the hydroxy value, the hydroxyvalue is preferably from 5 to 100 mgKOH/g, particularly preferably from10 to 80 mgKOH/g. When the hydroxy value is at least the above lowerlimit value, in a case where the cured film has a single layerstructure, it will be excellent in adhesion between the layer and thesubstrate, and in a case where the cured film has a two layer structure,it will be excellent in adhesion between a layer formed by thefluororesin (A) and a layer formed by the non-fluororesin (E). When thehydroxy value is at most the above upper limit value, the cured filmwill be excellent in crack resistance under temperature cycles between ahigh temperature of at least 100° C. and a low temperature of at most10° C. Measurement of the hydroxy value is carried out in accordancewith JIS K1557-1 (2007 edition).

In a case where the fluororesin (A) has carboxy groups, the acid valueof the fluororesin (A) is preferably from 0.1 to 50 mgKOH/g, morepreferably from 1.0 to 4.0 mgKOH/g. When the acid value of thefluororesin (A) is at least the above lower limit value, it will beeffective in improving dispersibility of a pigment, and when it is atmost the above upper limit value, the cured film will be excellent inmoisture resistance. Measurement of the acid value is conducted inaccordance with JIS K5601-2-1 (2009).

In a case where the fluororesin (A) or the non-fluororesin (E) in thepowder paint of the present invention is a polymer containing unitshaving chlorine atoms, it is possible that in the resin structure of thepowder paint, chlorine atoms present as not chemically bonded(hereinafter referred to as “free Cl”) are likely to be contained. Suchfree CI is considered to be primarily derived from chlorine atomscontained in a chlorinated monomer as a raw material of the resin, orfrom chlorine components contained as impurities in chemical structuresof other additive components or in the respective components of theresin.

In what form such free CI is present in the fluororesin (A), is notnecessarily clearly understood, but a form of a metal salt may, forexample, be conceivable. When free CI is present, it is likely toincrease the molecular weights of the fluororesin (A) and other resinscontained in the powder paint, and as a result, likely to causeimpairment of the quality of the film surface formed from the powderpaint.

Therefore, in the present invention, the amount of free CI in the powderpaint is preferably controlled to be at a low level. The amount of freeCI is preferably from 0.1 to 30 mass ppm, more preferably from 0.5 to 25mass ppm, particularly preferably from 1.0 to 22.0 mass ppm, to thefluororesin (A). When the amount of free CI is at least the above lowerlimit value, orange peel of the cured film is less likely to be formed,and when it is at most the upper limit value, the cured film is lesslikely to be colored.

For the amount of free CI, the powder paint may dissolved in an organicsolvent capable of dissolving the resin component, then the organicsolvent may extracted with water to obtain an aqueous layer, whereuponthe amount of chlorine ions contained in the aqueous layer may bequantified by e.g. an ion chromatography method.

(Metal Element (B))

The powder paint of the present invention contains a specific amount ofat least one metal element selected from the group consisting ofpotassium, sodium and magnesium, as the metal element (B). Potassium,sodium and magnesium are incorporated into the powder paint in the formof metal salts.

The metal salts may, for example, be potassium salts such as potassiumcarbonate, potassium hydroxide, potassium bicarbonate, potassiummethoxide, potassium ethoxide, potassium phosphate, etc.; sodium saltssuch as sodium hydroxide, sodium hydrogen carbonate, sodium carbonate,sodium methoxide, sodium ethoxide, sodium phosphate, etc.; magnesiumsalts such as magnesium hydroxide, magnesium carbonate, magnesiumphosphate, etc.

In a case where the metal salt is incorporated into the powder paint ofthe present invention, the form of the metal salt present in the powderpaint is not particularly limited, and it may be present in variousforms, for example, in the form of a metal salt as it is, or in the formas chemically bonded to another component.

The concentration of the metal element (B) in the powder paint is from2.0 to 60 mass ppm, preferably from 2.1 to 50 mass ppm, more preferablyfrom 2.2 to 40 mass ppm, to the fluororesin (A). When the concentrationof the metal element (B) is at least the above lower limit value, evenif melt kneading is repeated in a plurality of times in the production,increase in the molecular weight of the fluororesin (A) tends to besmall, and the stability of the powder paint tends to be high. On theother hand, when it is at most the above upper limit value, a haze ofthe cured film is less likely to occur.

Further, the mass ratio of the metal element (B) to free CI ispreferably from 1.0 to 10.0, more preferably from 1.1 to 9.0,particularly preferably from 1.2 to 8.0. When the mass ratio is at leastthe above lower limit value, even if the melt-kneading temperature ismade to be as high as at least 200° C., it is possible to suppressincrease in the molecular weight of the fluororesin (A). On the otherhand, when it is at most the above upper limit value, a tough cured filmcan be obtained.

(Light Stabilizer (C))

The powder paint of the present invention contains a light stabilizer(C) in a specific amount. The light stabilizer (C) is one to beincorporated in order to prevent degradation of the resins (thefluororesin (A) and the non-fluororesin (E)) in the cured film. Forexample, by capturing radical species generated in a cured film byultraviolet light, it is possible to prevent further deterioration.

As the light stabilizer (C), preferred is a hindered amine lightstabilizer having a number-average molecular weight of from 300 to 5,000and a melting point of from 50 to 250° C., since it will be therebyreadily locally distributed in the layer formed by the non-fluororesin(E) during the curing process. From such a viewpoint that it can bereadily uniformly diffused in the powder paint during kneading, ahindered amine light stabilizer having a molecular weight of from 400 to4,000 and a melting point of from 60 to 200° C. is particularlypreferred.

As the light stabilizer (C), one type may be used alone, or two or moretypes may be used in combination.

Commercially available hindered amine light stabilizers may, forexample, be “Tinuvin (registered trademark) 111FDL” (molecular weight:2,000 to 4,000, melting point: 63° C.), “Tinuvin (registered trademark)144” (molecular weight: 685, melting point: 146 to 150° C.), “Tinuvin(registered trademark) 152” (molecular weight: 756.6, melting point: 83to 90° C.), manufactured by BASF; “Sanduvor (registered trademark) 3051powder” (molecular weight: 364.0, melting point: 225° C.), “Sanduvor(registered trademark) 3070 powder” (molecular weight: 1,500, meltingpoint: 148° C.), “VP Sanduvor (registered trademark) PR-31” (molecularweight: 529, melting point: 120 to 125° C.), manufactured by Clariant;etc.

The concentration of the light stabilizer (C) in the powder paint isfrom 10 to 10,000 mass ppm, preferably from 100 to 5,000 mass ppm, morepreferably from 500 to 3,000 mass ppm, to the fluororesin (A). When theconcentration of the light stabilizer (C) is at least the above lowerlimit value, orange peel is less likely to be formed in the cured film,and on the other hand, when it is at most the above upper limit value,in a case where cyanine blue is added, the dark blue paint color is lesslikely to be yellowish.

(Polymerization Inhibitor (D))

The powder paint of the present invention contains a specific amount ofa polymerization inhibitor (D). The polymerization inhibitor (D) in thepowder paint may, for example, be a polymerization inhibitor of e.g. ahydroquinone-type, catechol-type, anthraquinone-type,phenothiazine-type, hydroxy toluene-type, etc. Among them, ahydroquinone-type polymerization inhibitor is preferred, andhydroquinone is particularly preferred, since it is thereby easy toprevent increase in the molecular weight of the fluororesin (A).

The concentration of the polymerization inhibitor (D) in the powderpaint is from 10 to 5,000 mass ppm, preferably from 50 to 3,000 massppm, more preferably from 100 to 2,000 mass ppm, to the fluororesin (A).When the concentration of the polymerization inhibitor (D) is at leastthe above lower limit value, in a case where the polymerizationinhibitor (D) is added during the polymerization reaction of the resin,it tends to be easy to prevent generation of free CI from the resin, andon the other hand, when it is at most the above upper limit, the curedfilm is less likely to be colored.

(Non-Fluororesin (E))

The powder paint of the present invention may contain resins other thanthe fluororesin (A). As the resins other than the fluororesin (A), afluororesin other than the fluororesin (A), and a non-fluororesin (E)may be mentioned, and a non-fluororesin (E) is preferred.

The non-fluororesin (E) may, for example, be at least one memberselected from the group consisting of an acrylic resin, a polyesterresin, an urethane resin, an epoxy resin and a silicone resin. Amongthem, an acrylic resin or a polyester resin is preferred, and apolyester resin is particularly preferred, because of excellent adhesionto a substrate, and since the fluororesin (A) and the non-fluororesin(E) tend to readily undergo phase separation when formed into a curedfilm, and from the viewpoint of excellent light resistance. Preferably,the polyester resin is particularly preferred.

<Acrylic Resin>

The acrylic resin is a polymer having units based on a (meth) acrylate.The acrylic resin may, for example, be an acrylic resin having areactive group such as a carboxy group, a hydroxy group, a sulfo group,etc. The acrylic resin can improve the dispersibility of a pigment.

The glass transition temperature of the acrylic resin is preferably from30 to 60° C. When the glass transition temperature is at least the abovelower limit value, blocking is less likely to occur, and when it is atmost the above upper limit value, the surface smoothness of the curedfilm will be more excellent.

The number average molecular weight of the acrylic resin is preferablyfrom 5,000 to 100,000, particularly preferably from 30,000 to 100,000.When the number average molecular weight of the acrylic resin is atleast the above lower limit value, blocking is less likely to occur, andwhen it is at most the above upper limit value, it is possible tofurther improve the surface smoothness of the cured film.

The mass average molecular weight of the acrylic resin is preferablyfrom 6,000 to 150,000, more preferably from 40,000 to 150,000,particularly preferably from 60,000 to 150,000. When the mass averagemolecular weight of the acrylic resin is at least the above lower limitvalue, blocking is less likely to occur, and when it is at most theabove upper limit, it is possible to further improve the surfacesmoothness of the cured film.

In a case where the acrylic resin has carboxy groups, the acid value ofthe acrylic resin is preferably from 150 to 400 mgKOH/g. When the acidvalue of the acrylic resin is at least the above lower limit value, itis effective in improving dispersibility of a pigment, and when it is atmost the above upper limit, the cured film will be excellent in moistureresistance.

Commercially available acrylic resins may, for example, be “FINEDIC(registered trademark) A-249”, “FINEDIC (registered trademark) A-251”and “FINEDIC (registered trademark) A-266”, manufactured by DIC Corp.;“ALMATEX (registered trademark) PD6200” and “ALMATEX (registeredtrademark) PD7310”, manufactured by Mitsui Chemicals, Inc.; “SANPEXPA-55” manufactured by Sanyo Chemical Industries Ltd.; etc.

<Polyester Resin>

The polyester resin has units based on a dehydration reaction product ofa polyvalent carboxylic acid compound and a polyhydric alcohol compound,and as the case requires, may have units other than these two types ofunits (such as units based on a hydroxycarboxylic acid compound). Thepolyester resin has at least either a carboxy group or a hydroxy groupat terminals of the polymer chain.

The polyvalent carboxylic acid compound may, for example, be phthalicacid, isophthalic acid, terephthalic acid, naphthalene dicarboxylicacid, trimellitic acid, pyromellitic acid, phthalic anhydride, etc., andisophthalic acid is preferred in that the cured film will be therebyexcellent in weather resistance.

As the polyhydric alcohol compound, an aliphatic polyhydric alcohol oran alicyclic polyhydric alcohol is preferred, and an aliphaticpolyhydric alcohol is more preferred, from the viewpoint of excellentadhesion to a substrate and excellent flexibility of the cured film.

The polyhydric alcohol compound may, for example, be ethylene glycol,diethylene glycol, triethylene glycol, 1,2-propanediol, 1,3-propanediol,1,3-butanediol, 1,4-butanediol, 1,2-pentanediol, 1,5-pentanediol,neopentyl glycol, spiro glycol, 1,10-decanediol,1,4-cyclohexanedimethanol, trimethylolethane, trimethylolpropane,glycerol, pentaerythritol, etc.

As the polyhydric alcohol, neopentyl glycol, 1,2-pentanediol,1,5-pentanediol, trimethylol propane or the like, is preferred, and fromthe viewpoint of ease of availability, neopentyl glycol or trimethylolpropane, is particularly preferred.

Commercially available polyester resins may, for example, be “CRYLCOAT(registered trademark) 4642-3” and “CRYLCOAT (registered trademark)4890-0”, manufactured by DAICEL-ALLNEX LTD.; “GV-250”, “GV-740” and“GV-175”, manufactured by Japan U-PICA Co., Ltd.; etc.

<Urethane Resin>

The urethane resin may be a mixture obtained by mixing, or a resinobtained by reacting, a polyol (such as acrylic polyol, polyesterpolyol, polyether polyol, propylene glycol, propylene oxide, etc.) andan isocyanate compound. In the present invention, it is preferred to usean urethane resin comprising a powdery polyol (acrylic polyol, polyesterpolyol or polyether polyol) and a powdery isocyanate compound.

<Epoxy Resin>

The epoxy resin may, for example, be a bisphenol A epoxy resin, abisphenol F type epoxy resin, etc.

Commercially available epoxy resins may, for example, be “EPIKOTE(registered trademark) 1001”, “EPIKOTE (registered trademark) 1002” and“EPIKOTE (registered trademark) 4004P”, manufactured by MitsubishiChemical Corporation; “EPICLON (registered trademark) 1050” and “EPICLON(registered trademark) 3050”, manufactured by DIC Corporation; “EPOTOHTO(registered trademark) YD-012” and “EPOTOHTO (registered trademark)YD-014”, manufactured by Nippon Steel & Sumikin Chemical Co., Ltd.;“Denacol (registered trademark) EX-711”, manufactured by Nagase ChemteXCorporation; “EHPE3150” manufactured by Daicel Corporation, Ltd.; etc.

<Silicone Resin>

The silicone resin may be one having a branched structure and havingsilanol groups (Si—OH) as reactive groups which undergo dehydrationcondensation with each other for curing, to form, after curing, a curedfilm having a three-dimensional crosslinked structure. Otherwise, asilicone resin having a relatively low molecular weight (a siliconeresin intermediate for modification) and another thermosetting resin(such as an alkyd resin, a polyester resin, an epoxy resin, an acrylicresin, etc.) may be used in combination.

Commercially available silicone resins may, for example, be “GLASCAHPC-7506”, manufactured by JSR Corporation; “Zemrack (registeredtrademark)”, manufactured by Kaneka Corporation, “SILIKOPON (registeredtrademark) EF”, “SILIKOPON (registered trademark) EW”, “SILIKOPON(registered trademark) EC” and “SILIKOPON™ ED”, manufactured by Evonik;etc.

The powder paint preferably contains from 10 to 400 parts by mass of anon-fluororesin (E) and particularly preferably contains from 20 to 300parts by mass of a non-fluororesin (E), per 100 parts by mass of thefluororesin (A). When the concentration of the non-fluororesin (E) is atleast the above lower limit value, even if the aluminum substrate is onetreated with a chromium-free chemical treatment agent, it is possible tosecure the adhesion to the substrate. On the other hand, when theconcentration of the non-fluororesin (E) is at most the above upperlimit value, the cured film will be excellent in weather resistance.

(Other Components)

The powder paint of the present invention preferably contains, inaddition to the above-described components, components for the purposeof improving the surface smoothness, weather resistance, durability,etc. of the cured film, as additives. As such additives, a curing agent,a curing catalyst, a pigment, an ultraviolet absorber, a surfaceadjusting agent (leveling agent), a degassing agent, a plasticizer, etc.may be mentioned. Further, depending on the particular purpose, it mayfurther contain a nonionic, cationic or anionic surfactant, a silanecoupling agent, a matting agent such as ultrafine synthetic silica, afiller, a heat stabilizer, a thickener, a dispersing agent, a chargeinhibitor, a rust inhibitor, an antifouling agent, a water repellentagent, a low-staining treatment agent, etc.

The powder paint of the present invention preferably contains a curingagent and a curing catalyst, as additives, since a cured film is therebyeasily obtainable.

The content of the additives may be suitably adjusted within a range notto impair the effects of the present invention, and it is usuallypreferably from 0.01 to 70 mass %, more preferably from 0.05 to 60 mass%, to the total amount (100 mass %) of the powder paint. Among theadditives, the content of additives, etc. other than the pigment and thecuring agent, is preferably from 0.01 to 10 mass %, more preferably from0.05 to 5 mass %, to the total amount (100 mass %) of the powder paint.

<Curing Agent>

The curing agent is a compound which reacts with reactive groups of theresin (the fluororesin (A) or non-fluororesin (E)), to cross-link theresin or to increase its molecular weight thereby to cure the resin. Thecuring agent is preferably used in a case where the resin has reactivegroups, and it is preferred to select one having two or more reactivegroups which are reactive with the reactive groups (hydroxy groups,carboxy groups, etc.) of the resin.

Further, the reactive groups of the curing agent are preferably oneswhich are less likely to react with the reactive groups of the resin atnormal temperature conditions, and which are reactive when the powderpaint is heated and melted. For example, at the time of selectingisocyanate groups as the reactive groups of the curing agent, it ispreferred to select blocked isocyanate groups rather than isocyanategroups having a higher reactivity at room temperature. When the powderpaint is heated and melted, blocked isocyanate groups become isocyanategroups as the blocking agent is desorbed, and the isocyanate groups willthen act as reactive groups.

As such a curing agent, a known compound may be used. For example, ablocked isocyanate curing agent, an amine type curing agent (melamineresin, guanamine resin, sulfonamide resin, urea resin, aniline resin,etc.), a (3-hydroxyalkylamide curing agent, a triglycidyl isocyanuratecuring agent, etc. may be mentioned. A blocked isocyanate curing agentis particularly preferred in that adhesion to a substrate,processability of a product after coating, water resistance of a curedfilm, etc. will be thereby excellent.

In a case where the fluororesin (A) has hydroxy groups as reactivegroups, the curing agent is preferably a blocked isocyanate curingagent.

In a case where the fluororesin (A) has only carboxy groups as reactivegroups, the curing agent is preferably a p-hydroxyalkylamide curingagent, or a triglycidyl isocyanurate curing agent.

As the curing agent, one type may be used alone, or two or more typesmay be used in combination.

The softening temperature of the curing agent is preferably from 10 to120° C., particularly preferably from 40 to 100° C. When the softeningtemperature is at least the above lower limit value, the powder paint isless likely to be cured at room temperature, and particulateagglomerates are less likely to be formed. When the softeningtemperature is at most the above upper limit value, when raw material ismelt-kneaded to produce a powder, the curing agent will be easilyhomogeneously dispersed in the powder, the surface smoothness of thecured film to be formed will be better, and in addition, the cured filmwill be excellent in strength, moisture resistance, etc.

The blocked isocyanate curing agent is preferably one which is solid atroom temperature.

The blocked isocyanate curing agent is preferably one which is producedby reacting an aliphatic, aromatic or araliphatic diisocyanate and alow-molecular compound having active hydrogen to obtain apolyisocyanate, which is then reacted with a blocking agent for masking.

The diisocyanate may, for example, be tolylene diisocyanate,4,4′-diphenylmethane diisocyanate, xylylene diisocyanate, hexamethylenediisocyanate, 4,4′-methylenebis(cyclohexyl isocyanate),methylcyclohexane diisocyanate, bis(isocyanatomethyl) cyclohexaneisophorone diisocyanate, dimer acid diisocyanate, lysine diisocyanate,etc.

The low molecular compound having active hydrogen may, for example, bewater, ethylene glycol, propylene glycol, trimethylolpropane, glycerin,sorbitol, ethylenediamine, ethanolamine, diethanolamine,hexamethylenediamine, isocyanurate, uretdione, a low molecular weightpolyester having hydroxy groups, polycaprolactone, etc.

The blocking agent may, for example, be an alcohol (methanol, ethanol,benzyl alcohol, etc.), a phenol (phenol, cresol etc.), a lactam(caprolactam, butyrolactam, etc.), an oxime (cyclohexanone, oxime,methyl ethyl ketoxime, etc.), etc.

<Curing Catalyst>

The curing catalyst is one which promotes the curing reaction andimparts excellent chemical properties and physical properties to thecured film.

For example, in a case where the powder paint contains a blockedisocyanate curing agent, the curing catalyst is preferably a tincatalyst (stannous octoate, tributyltin laurate, dibutyltin dilaurate,etc.).

As the curing catalyst, one type may be used alone, or two or more typesmay be used in combination.

<Pigment>

The pigment is preferably at least one member selected from the groupconsisting of a luster pigment, an anticorrosive pigment, a coloringpigment and an extender pigment.

The luster pigment is a pigment for lustering a cured film. The lusterpigment may, for example, be aluminum powder, nickel powder, stainlesssteel powder, copper powder, bronze powder, gold powder, silver powder,mica powder, graphite powder, glass flakes, scale-like iron oxidepowder, etc.

The anticorrosive pigment is a pigment for preventing corrosion ordeterioration of a substrate which is required to have corrosionresistance. As the anticorrosive pigment, a lead-free anticorrosivepigment is preferred which presents little impact on the environment.The lead-free anti-corrosive pigment may, for example, be zinccyanamide, zinc oxide, zinc phosphate, calcium magnesium phosphate, zincmolybdate, barium borate, zinc calcium cyanamide, etc.

The coloring pigment is a pigment for coloring the cured film. Thecoloring pigment may, for example, be titanium oxide, carbon black, ironoxide, phthalocyanine blue, phthalocyanine green, quinacridone,isoindolinone, benzimidazolone, dioxazine, etc.

The extender pigment is a pigment to improve the hardness of the curedfilm and to increase the thickness of the cured film. Further, it ispreferably incorporated in that when the substrate is cut, the cutsurface of the cured film can be made clean. The extender pigment may,for example, be talc, barium sulfate, mica, calcium carbonate, etc.

<Ultraviolet Absorber>

As the ultraviolet absorber, any ultraviolet absorber selected fromorganic ultraviolet absorbers and inorganic ultraviolet absorbers may beused.

As the ultraviolet absorber, one type may be used alone, or two or moretypes may be used in combination.

The organic ultraviolet absorbents may, for example, be salicylateultraviolet absorbers, benzotriazole ultraviolet absorbers, benzophenoneultraviolet absorbers, cyanoacrylate ultraviolet absorbers, etc.

As the organic ultraviolet absorber, a compound having a molecularweight of from 200 to 1,000 is preferred. When the molecular weight isat least 200, it is possible to remain in the cured film without beingvolatilized in the melting and curing process of the powder paint. Whenthe molecular weight is at most 1,000, in a case where the cured filmhas a two-layer structure, it can remain in the layer formed by thefluororesin (A).

As the organic ultraviolet absorber, a compound having a melting pointof from 50 to 150° C. is preferred. When the melting point is at least50° C., it is possible to remain in the cured film without beingvolatilized in the melting and curing process of the powder paint. Whenthe melting point is at most 150° C., it tends to be easily melted inthe melting and curing process of the powder paint, and in a case wherethe cured film has a two-layer structure, it can remain in the layerformed by the fluororesin (A).

Commercially available organic ultraviolet absorbers may, for example,be “Tinuvin (registered trademark) 326” (molecular weight: 315.8,melting point: 139° C.), “Tinuvin (registered trademark) 405” (molecularweight: 583.8, melting point: 74 to 77° C.), “Tinuvin (registeredtrademark) 460” (molecular weight: 629.8, melting point: 93 to 102° C.),“Tinuvin (registered trademark) 900” (molecular weight: 447.6, meltingpoint: 137 to 141° C.) and “Tinuvin (registered trademark) 928”(molecular weight: 441.6, melting point: 109 to 113° C.), manufacturedby BASF; “Sanduvor (registered trademark) VSU powder” (molecular weight:312.0, melting point: 123 to 127° C.), manufactured by Clariant Corp.;“Hastavin (registered trademark) PR-25 Gran” (molecular weight: 250.0,melting point: 55 to 59° C.), manufactured by Clariant Corp.; etc.

The inorganic ultraviolet absorbers may, for example, be filler-typeinorganic ultraviolet absorbers including ultraviolet absorbing oxides(zinc oxide, cerium oxide, etc.).

As the inorganic ultraviolet absorber, preferred may, for example, becomposite particles of titanium oxide and zinc oxide, compositeparticles of titanium oxide and cerium oxide, composite particles ofzinc oxide and cerium oxide, composite particles of titanium oxide, zincoxide and cerium oxide, etc.

<Surface Conditioner>

The surface conditioner (also referred to as a leveling agent) is onehaving an effect to improve the surface smoothness of the cured film.

Commercially available surface conditioners may, for example, be “BYK(registered trademark)-361N”, “BYK (registered trademark)-360P”, “BYK(registered trademark)-364P”, “BYK (registered trademark)-368P”, “BYK(registered trademark)-3900P”, “BYK (registered trademark)-3931P”, “BYK(registered trademark)-3933P”, “BYK (registered trademark)-3950P”, “BYK(registered trademark)-3951P” and “BYK (registered trademark)-3955P”,trade names, manufactured by BYK-Chemie, etc.

<Degassing Agent>

The degassing agent is one having an effect to prevent e.g. aircontained in the powder paint, or a blocking agent, moisture, etc. inthe case of using a blocked isocyanate curing agent as the curing agent,from remaining inside of the cured film. The degassing agent may, forexample, be benzoin, etc.

<Plasticizer>

The plasticizer is one having an effect to improve the surfacesmoothness, adhesion to a substrate, impact resistance, etc. of thecured film. The plasticizer may, for example, be dicyclohexyl phthalate,hexabromocyclododecane, tri-benzoic acid glyceride, tetrabenzoic acidpentaerythritol, 1,4-cyclohexane dimethanol dibenzoate, etc.

[Painted Article]

A painted article has a cured film formed by the above-described powderpaint on the surface of a substrate.

The material for the substrate is preferably a metal such as aluminum,iron, magnesium, etc., and aluminum is particularly preferred, since itis excellent in corrosion resistance and light in weight, and presentsan excellent performance in application as building material.

The shape, size, etc. of the substrate, are not particularly limited.

The thickness of the cured film is not particularly limited, but isusually at most 200 μm, preferably from 1 to 100 μm.

The powder paint of the present invention is excellent in weatherresistance, and thus can be used for the exterior of e.g. buildingswhich are exposed to harsh environments. For example, it can be used asthe exterior of goods which are required to have high weatherresistance, such as an outdoor unit of air conditioner, a pole oftraffic signal, a sign board, etc. that are installed along the coast.The thickness of the cured film in these applications is preferably from30 to 200 μm, more preferably 40 to 150 μm. The thickness of the curedfilm is measured by the method of JIS K5600-1-7 (2009).

The water contact angle of the cured film is preferably from 1 to 55°,particularly preferably from 3 to 50°. When the water contact angle ofthe cured film is at least the above lower limit value, the cured filmis less likely to be eroded by organic acid components resulting fromdroppings of birds or dead bodies of insects, and occurrence of mold onthe cured film surface can be prevented (occurrence of mold tends tolead to poor appearance). When the water contact angle of the cured filmis at most the above upper limit value, the cured film is excellent instain resistance.

The water contact angle of the cured film is obtained by measuring acontact angle upon dropping a droplet of water on the coating film inair, by using a contact angle meter (CA-X model, manufactured by KyowaInterface Science Co., Ltd.).

In a case where the powder paint contains a non-fluororesin (E), thecured film formed by the powder paint may be in the form of one-layerstructure wherein the fluororesin (A) and the non-fluororesin (E) arepresent as mixed, or may be in the form of a two-layer structure whereinthe fluororesin (A) and the non-fluororesin (E) form separate layers.The two-layer structure is preferred, since the cured film will befurther excellent in chemical resistance and weather resistance. Amethod for forming the cured film of such a two-layer structure may, forexample, be the method as disclosed in WO2014/002964.

[Method of Producing Powder Paint]

The powder paint can be prepared by known methods. For example, thefollowing methods may be mentioned.

Method I: A method wherein the raw materials i.e. the fluororesin (A), ametal salt for the metal element (B), the light stabilizer (C), thepolymerization inhibitor (D), etc. are, respectively, preliminarilypulverized into powder, followed by mixing.

Method II: A method wherein the above raw materials are mixed in thesolid state, followed by pulverization into powder.

Method III: A method wherein the above raw materials are mixed in thesolid state, then melt-kneaded, and then cooled to a massive form,followed by pulverization into powder.

Among them, method III is preferred, since in the resulting powder, therespective components are uniformly distributed, whereby it is possibleto obtain a cured film excellent in uniformity.

Otherwise, the metal salt for the metal element (B), the lightstabilizer (C) and the polymerization inhibitor (D) may be added to thereaction solution during the polymerization reaction in the productionof the fluororesin (A), or they may be added to the reaction solutionafter the polymerization reaction and before removing the solvent.However, in a case where the monomer raw material of the fluororesin (A)contains a chlorine-containing monomer, the polymerization inhibitor (D)is preferably added after the polymerization reaction, with a view topreventing occurrence of free CI from the chlorine-containing monomer.The polymerization reaction may be carried out by a known method.

In a case where the metal salt for the metal element (B) and the lightstabilizer (C) are added to the reaction solution during thepolymerization reaction in the production of the fluororesin (A) ornon-fluororesin (E), or immediately after the polymerization reaction,it is preferred that the solvent in the reaction mixture is thereafterremoved. Removal of the solvent is carried out by a known technique suchas vacuum drying.

Mixing of the raw materials can be conducted by using a known mixer. Thetype of the mixer may, for example, be a high-speed mixer, a V typemixer, an inversion mixer, etc.

Melt-kneading can be carried out by using an extruder of various typessuch as single screw, twin screw, planetary gear, etc. A mixture of therespective components is preferably kneaded in a heated and meltedstate, in order to mix the respective components uniformly. Themelt-kneaded product extruded is preferably cooled and pelletized.

Pulverization of pellets can be conducted by using a known pulverizer.The type of the pulverizer may, for example, be a pin mill, a hammermill, a jet mill, etc.

After the pulverization, it is preferred to carry out classification. Inthe case of carrying out classification, it is preferred to removeeither particles with a size of less than 10 μm, or particles with asize exceeding 100 μm.

The average particle size of particles contained in the powder paint is,for example, preferably from about 20 to 60 μm, more preferably from 25to 50 μm, by 50% average volume particle size distribution. The particlesize is measured by using a particle size measuring instrument which iscommonly used. The system of the particle size measuring instrument may,for example, be a system to capture a potential change at the time ofpassing through pores, a laser diffraction system, an image judgmentsystem, a sedimentation rate measurement system, etc.

In a case where the powder paint of the present invention contains anon-fluororesin (E), or additives such as a curing agent, a pigment, acuring catalyst, an ultraviolet absorber, a surface controlling agent,etc., the mixing, melt kneading and pulverization thereof can be carriedout in the same manner as described above.

(Method of Procuring Painted Article)

The painted article is produced by forming a cured film by theabove-described powder paint on the surface of a substrate.

Formation of the cured film may be accompanied or may not be accompaniedby a curing reaction of the fluororesin (A) and/or non-fluororesin (E)with a curing agent. For example, it is possible to form a cured film byapplying a heated molten powder paint onto a substrate surface to form acoating film on the substrate surface, followed by cooling forsolidification to room temperature (20 to 25° C.).

The method for applying the heated molten powder paint on the substratesurface, may be a method wherein the powder paint is heated and melted,and then applied onto the substrate surface, or a method wherein thepowder paint is applied on the substrate surface, and then heated andmelted. In the case of the method wherein the powder paint is heated andmelted, and then applied onto the substrate surface, curing will proceedat the same time as the powder paint is heated and melted, andtherefore, it is preferred to conduct the heating and meltingimmediately before the application.

The heating temperature (hereinafter referred to also as “bakingtemperature”) and the heating retention time (hereinafter referred toalso as “baking time”) for heating and melting the powder paint andmaintaining its molten state for a predetermined time, are suitably setdepending upon the types and composition of raw material components ofthe powder paint, the film thickness, etc. of the desired cured film,etc.

In particular, the baking temperature is preferably set depending on thereaction temperature of the curing agent to be used. For example, in thecase of using a blocked polyisocyanate curing agent as the curing agent,the baking temperature is preferably from 170 to 210° C., morepreferably from 180 to 200° C. The baking time is preferably from 5 to120 minutes, particularly preferably from 10 to 60 minutes.

Cooling after the baking may be either rapid cooling or slow cooling,but slow cooling is preferred, in that interfacial peeling due to thedifference in curing shrinkage between the layer formed by thefluororesin (A) and the layer formed by the non-fluororesin (E) isthereby less likely. The slow cooling rate is from 1 to 30° C./min,preferably from 2 to 20° C./min.

As the coating method, it is possible to use an electrostatic coatingmethod, an electrostatic spraying method, an electrostatic immersionmethod, a misting method, a fluidized bed coating method, a blowingmethod, a spraying method, a thermal spraying method, a plasma sprayingmethod, etc.

An electrostatic coating method using a powder coating gun is preferredin that even when the cured film is made thin, the cured film isexcellent in smoothness, and further in that the cured film is excellentin concealing properties. The powder coating gun may, for example, be acorona charging type spray gun or a triboelectric charging type spraygun. The corona charging type spray gun is one whereby the powder paintis subjected to corona discharge treatment and sprayed, and thetriboelectric charging type coating gun is one whereby the powder paintis subjected to triboelectric charging treatment and sprayed.

The ejection amount of the powder paint from the powder coating gun ispreferably set to be from 50 to 200 g/min, more preferably from 55 to180 g/min. The distance from the tip of the gun portion of the powdercoating gun to the substrate is preferably set to be from 150 to 400 mm,more preferably from 200 to 350 mm, from the viewpoint of coatingefficiency,

At the time of ejecting the powder paint from the corona charging typecoating gun for coating, the load voltage to be applied to thecomponents constituting the powder paint by the corona dischargetreatment, is set to be preferably from −50 to −100 KV, furtherpreferably from −60 to −80 KV from the viewpoint of excellent coatingefficiency (the deposition rate of the powder paint on the substrate)and excellent appearance of the cured film.

On the other hand, at the time of ejecting the powder paint from thetriboelectric charging type coating gun, the triboelectric chargingtreatment is carried out so that the internally generated current valueof the powder paint will be preferably from 1 to 8 μA, more preferablyfrom 1.1 to 7 μA from the viewpoint of excellent coating efficiency andexcellent appearance of the cured film.

In a case where the electrostatic coating method is to be industriallyimplemented, for example, in order to set and ground a non-coatedmirror, a grounded conductive horizontal belt conveyor is installed in acoating chamber, and a gun is set at an upper portion in the coatingchamber. Here, the painting pattern width is preferably from 50 to 500mm, the operating speed of the gun is preferably from 1 to 30 m/m in,and the conveyor speed is preferably from 1 to 50 m/min, and from theabove preferred ranges, suitable conditions may be selected for usedepending upon the particular purpose.

As a method of forming a cured film having a relatively thick thickness,a fluidized bed coating method is preferred. In the fluidized bedcoating method, a substrate having a surface to be coated, heated to atemperature of at least the melting temperature of the powder paint, isdipped in a fluidized bed in which the powder flowing as carried by agas such as air, is accommodated, to let the powder deposit on thesurface to be coated of the substrate, and be melted thereby to let acoating film having a predetermined thickness be formed on thesubstrate, whereupon the coated substrate is taken out from thefluidized bed, and in some cases, the molten state of the coating filmis maintained for a predetermined period of time. Thereafter, thecoating film in the molten state is preferably cooled and solidified toobtain the substrate having a cured film formed thereon. The thicknessof the cured film to be formed in the fluidized bed coating method, isnot particularly limited, but is preferably from 100 to 1,000 μm, morepreferably from 150 to 900 μm.

The temperature in the fluidized bed in the fluidized bed coating methodis preferably from 15 to 55° C., and the temperature of the gas such asair blown into the bed in order to fluidize the powder, is alsopreferably from 15 to 55° C. The temperature of at least the surface tobe coated, of the substrate at the time of dipping in the fluidized bed,is preferably from 300 to 450° C., and the time for dipping thesubstrate in the fluidized bed is preferably from 1 to 120 seconds. Thesubstrate taken out from the fluidized bed is preferably maintained at atemperature of from 150 to 250° C. for from 1 to 5 minutes and thencooled to room temperature.

As described above, according to the powder paint of the presentinvention, increase in the molecular weight of the fluororesin at thetime of producing the powder paint composition can be suppressed,whereby a cured film formed therefrom is less likely to have abnormalappearance such as orange peel.

EXAMPLES

Now, the present invention will be described in detail with reference toExamples, but the present invention is by no means limited to theseExamples.

[Measuring Methods]

<Fluororesin Content>

1 g of a powder paint was dissolved in butyl acetate, and a pigmentcontent was precipitated by centrifugal separation. The supernatant wasdried to recover the resin component.

The recovered resin component was measured by ¹³C-NMR to determine thefluororesin content.

The measurement conditions by ¹³C-NMR are as follows.

Measuring device: digital NMR AVANCE III 400, manufactured by BrukerCorp.

Measurement method: NOESY (pulse width 30°, relaxation time: 10 seconds)

Measurement solvent: deuterated chloroform (CDCl₃)

Measurement temperature: room temperature

<Content of Free Chlorine Atoms (Free Cl)>

1 g of a powder paint was dissolved in 5 mL of toluene, and then, 3 mLof ultrapure water was added thereto, followed by shaking vigorously forthree minutes.

Further, by means of a centrifugal separator, a separation operation wascarried out at 12,000 rpm for 10 minutes.

After removing the toluene layer, water of the lower layer was diluted10 times, and the content of freed chlorine atoms was measured by an ionchromatograph (ICS-3000, manufactured by Thermo Fisher Co.) to calculatethe content relative to the fluororesin.

<Metal Element Content>

0.5 g of a powder paint was put in a platinum crucible and ashed byheating in an electric furnace. Then, it was dissolved in 1N nitric acidand diluted with 19 mL of ultrapure water, whereupon the metal elementcontent was measured by an atomic absorption spectrometry (AA-7000F,manufactured by Shimadzu Corporation) to calculate the content relativeto the fluororesin.

<Contents of Light Stabilizer and Polymerization Inhibitor>

With respect to a powder paint, by means of an ion chromatography, thecontents of a light stabilizer and a polymerization inhibitor weremeasured under the following conditions, to calculate the respectivecontents relative to the fluororesin.

Measuring device: manufactured by Agilent Technologies Inc. (Agilent1280 HPLC/6460MS)

Column: cadenza CD-C18 (2 mmφ×100 mm), manufactured by Imtakt Co.,

Eluent: 0.1 vol % formic acid aqueous solution

Flow rate: 0.3 mL/min

Column oven: 35° C.

Detector: UV280 nm

<Production Stability of Powder Paint>

Production stability of a powder paint was evaluated as follows.

The powder paint was melt-kneaded by a twin-screw extruder (16 mmextruder, manufactured by Thermo Prism Ltd.) at a barrel set temperatureof 120° C.

Before and after the melt-kneading, the number average molecular weightof the fluororesin was measured by GPC (HLC-8220, manufactured by TosohCorporation). Based on the following formula (3), the rate of increasein the number average molecular weight of the fluororesin aftermelt-kneading to the number average molecular weight of the fluororesinbefore melt-kneading (hereinafter referred to simply as “increase rate”)is determined, and the production stability was evaluated by thefollowing evaluation standards.Increase rate (%)=[(number average molecular weight of fluororesin aftermelt-kneading)/(number average molecular weight of fluororesin beforemelt-kneading)]×100  (3)“Evaluation Standards”

◯ (Good): The increase rate is less than 120%.

X (Bad): The increase rate is 120% or more.

Example 1 Production of Powder Paint

Into a stainless steel autoclave having an inner volume of 250 mL,equipped with a stirrer, 51.2 g of cyclohexyl vinyl ether, 13.3 g of4-hydroxybutyl vinyl ether, 55.8 g of xylene, 15.7 g of ethanol, 5.82 gof potassium carbonate, 0.7 g of a 50 mass % xylene solution oftert-butyl peroxypivalate and 63 g of chlorotrifluoroethylene (CTFE)were introduced. The temperature was gradually raised, and afterreaching 55° C., that temperature was maintained for 20 hours. Afterthat, the temperature was raised to 65° C. and kept for 5 hours. Then,after cooling to room temperature, 0.39 g of a hindered amine lightstabilizer (Tinuvin™ 144, manufactured by BASF), and 0.13 g ofhydroquinone as a polymerization inhibitor were added and stirred for 1hour. Thereafter, the residue was removed by filtration, followed byvacuum drying to obtain a powder paint (1).

The contents of free Cl, metal elements, the light stabilizer and thepolymerization inhibitor, in the obtained powder paint (1), the numberaverage molecular weight of the fluororesin before melt-kneading, andthe production stability of the powder paint, were evaluated inaccordance with the above-described procedures.

<Appearance Evaluation of Cured Film>

38.0 g of the powder paint (1), 11.0 g (INDEX=1) of a blocked isocyanatecuring agent (“VESTAGON (registered trademark) B1530”, manufactured byEvonik) as a curing agent, 0.4 g of benzoin as a degassing agent, 1.1 gof a powder coating leveling agent (“BYK (registered trademark)-360P”,manufactured by BYK-Chemie) as a surface modifier, 0.005 g of adibutyltin dilaurate solution in xylene (10,000-fold diluted product) asa curing catalyst, and 35.0 g of titanium oxide (“Ti-Pure (registeredtrademark) R960”, manufactured by DuPont, titanium oxide content: 89mass %) as a pigment, were mixed in a powder state by using a high speedmixer, to obtain a mixture.

Then, the obtained mixture was melt-kneaded by means of a twin-screwextruder (16 mm extruder, manufactured by Thermo Prism Ltd.) at a barrelset temperature of 120° C., to obtain pellets.

Then, the obtained pellets were pulverized at room temperature by usinga pulverizer and subjected to classification with a mesh to obtain apowder paint (1′). The average particle size of the powder paint (1′)was about 40 μm.

Here, the average particle size is one obtained by calculation from the50% average volume particle size distribution and was measured andevaluated by means of Helos-Rodos, manufactured by Sympatec.

Using the powder coating (1′) thus obtained, a test specimen wasprepared. As a base material, an aluminum substrate was used. Thesurface of the aluminum substrate was subjected to chromate treatment.

On one surface of the aluminum substrate, electrostatic coating wasapplied by means of an electrostatic coating machine (trade name:GX3600C, manufactured by Onoda Cement Corporation), and held in a 200°C. atmosphere for 20 minutes, followed by cooling to room temperature,to obtain a test specimen having a cured film with a thickness of from55 to 65 μm formed.

Using the obtained test specimen, the condition of the surface wasvisually observed, and the appearance of the cured film was evaluated bythe following evaluation standards.

“Evaluation Standards”

◯ (Excellent): The cured film was excellent in surface smoothness, andsurface irregularities, repelling, defect in wettability to thesubstrate, etc. were not observed.

Δ (Good): The cured film was excellent in surface smoothness, butforeign matters or dullness and further bleeding out of additivecomponents on the surface of the cured film, were observed.

X (Bad): The cured film was poor in surface smoothness, and surfaceirregularities, repelling, defect in wettability to the substrate, etc.were observed.

The measurement results and evaluation results in Example 1 are shown inTable 1 together with the results in Examples 2 to 9 and ComparativeExamples 1 to 3.

TABLE 1 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Potassium content 22.0 21.0— 5.0 40.0 22.0 (mass ppm) Sodium content — — 20 — — — (mass ppm)Content of freed 5.1 4.9 5.1 3.0 5.0 5.1 chlorine atoms (mass ppm) FreeCI/B (mass ratio) 4.3 4.3 3.9 1.7 8.0 4.3 Content of light 2,800 2,9002,600 2,800 2,800 250 stabilizer (mass ppm) Content of 950 1,000 920 950950 950 polymerization inhibitor (mass ppm) Number average 20,000 20,00020,000 20,000 20,000 20,000 molecular weight of fluororesin beforemelt-kneading Production stability of ∘ ∘ ∘ ∘ ∘ ∘ powder paintAppearance of cured ∘ ∘ ∘ ∘ ∘ Δ film Comp. Comp. Comp. Ex. 7 Ex. 8 Ex. 9Ex. 1 Ex. 2 Ex. 3 Potassium content 22.0 22.0 22.0 1.7 20.0 19.0 (massppm) Sodium content — — — — — — (mass ppm) Content of freed 5.1 5.1 5.15.0 5.1 20.3 chlorine atoms (mass ppm) Free CI/B (mass ratio) 4.3 4.34.3 0.34 3.9 0.9 Content of light 1,000 5,000 2,800 2,500 — 3,000stabilizer (mass ppm) Content of 950 950 950 960 980 — polymerizationinhibitor (mass ppm) Number average 20,000 20,000 20,000 20,000 20,00020,000 molecular weight of fluororesin before melt-kneading Productionstability of ∘ ∘ ∘ x x x powder paint Appearance of cured ∘ Δ ∘ x x xfilm

Example 2

A powder paint (2) was obtained in the same manner as in Example 1except that 5.82 g of potassium carbonate was changed to 2.36 g ofpotassium hydroxide. The contents of the respective components and thenumber average molecular weight of the fluororesin before and after themelt-kneading were measured, and the production stability of the powderpaint (2) was evaluated. Further, in the same manner as in Example 1, apowder paint (2′) was obtained, then, a test specimen was prepared, andthe appearance of the cured film was evaluated.

Example 3

A powder paint (3) was obtained in the same manner as in Example 1except that 5.82 g of potassium carbonate was changed to 1.68 g ofpotassium hydroxide. The contents of the respective components and thenumber average molecular weight of the fluororesin before and after themelt-kneading were measured, and the production stability of the powderpaint (3) was evaluated. Further, in the same manner as in Example 1, apowder paint (3′) was obtained, then, a test specimen was prepared, andthe appearance of the cured film was evaluated.

Examples 4 and 5

Powder paints (4) and (5) were obtained in the same manner as in Example1 except that 5.82 g of the addition amount of potassium carbonate waschanged to 1.32 g and 10.58 g, respectively. The contents of therespective components and the number average molecular weights of theFluororesins before and after the melt-kneading were measured, and theproduction stability of the powder paints (4) and (5) was evaluated.Further, in the same manner as in Example 1, powder paints (4′) and (5′)were obtained, then test specimens were prepared, and the appearance ofthe cured films was evaluated.

Examples 6 to 8

Powder paints (6) to (8) were obtained in the same manner as in Example1 except that 0.39 g of the hindered amine light stabilizer was changedto 0.03 g, 0.14 g, and 0.70 g, respectively. The contents of therespective components and the number average molecular weights of theFluororesins before and after the melt-kneading were measured, and theproduction stability of the powder paints (6) to (8) was evaluated.Further, in the same manner as in Example 1, powder paints (6′) to (8′)were obtained, then test specimens were prepared, and the appearance ofthe cured films was evaluated.

Example 9

A powder paint (9′) was prepared in the same manner as in Example 1except that to the powder paint (1′), 16.0 g of a polyester resin(“CRYLCOAT (registered trademark) 4890-0”, manufactured by DAICEL-ALLNEXLTD., weight average molecular weight: 4,400, number average molecularweight: 2,500, hydroxyl value: 30 mgKOH/g) was further added as anon-fluororesin. Then, a test specimen was prepared, and the appearanceof the cured film was evaluated.

Comparative Example 1

A powder paint (10) was obtained in the same manner as in Example 1except that the addition amount of potassium carbonate was changed from5.82 g to 0.5 g. The contents of the respective components and thenumber average molecular weight of the fluororesin before and after themelt-kneading were measured, and the production stability of the powderpaint was evaluated. Further, in the same manner as in Example 1, apowder paint (10′) was obtained, then a test specimen was prepared, andthe appearance of the cured film was evaluated.

Comparative Example 2

A powder paint (11) was obtained in the same manner as in Example 1except that a hindered amine light stabilizer was not used. The contentsof the respective components and the number average molecular weight ofthe fluororesin before and after the melt-kneading were measured, andthe production stability of the powder paint (11) was evaluated.Further, in the same manner as in Example 1, a powder paint (11′) wasobtained, then a test specimen was prepared, and the appearance of thecured film was evaluated.

Comparative Example 3

A powder paint (12) was obtained in the same manner as in Example 1except that no hydroquinone was used. The contents of the respectivecomponents and the number average molecular weight of the fluororesinbefore and after the melt-kneading were measured, and the productionstability of the powder paint was evaluated. Further, in the same manneras in Example 1, a powder paint (12′) was obtained, then a test specimenwas prepared, and the appearance of the cured film was evaluated.

The results of the measurements and evaluations in the above Examples 2to 9 and Comparative Examples 1 to 3 are shown in Table 1.

As shown in Table 1, the molecular weights of the Fluororesins beforethe melt-kneading in Examples 1 to 9 and Comparative Examples 1 to 3were the same.

Further, the powder paints in Examples 1 to 9 showed a low increase inthe molecular weight after the melt-kneading and thus were excellent inthe production stability. In contrast, the powder paints in ComparativeExample 1 wherein the content of potassium atoms or sodium atoms wassmall, in Comparative Example 2 wherein no light stabilizer wascontained, and in Comparative Example 3 wherein no polymerizationinhibitor was contained, showed a high increase in the molecular weightafter the melt kneading and thus were inferior in the productionstability.

Further, the cured films formed from the powder paints in Examples 1 to9 were free from occurrence of orange peel, and the cured films wereexcellent in appearance. In contrast, the cured films formed from thepowder paints in Comparative Example 1 wherein the content of potassiumatoms or sodium atoms was small, in Comparative Example 2 wherein nolight stabilizer was contained, and in Comparative Example 3 wherein nopolymerization inhibitor was contained, had occurrence of orange peel,and the cured films were poor in appearance.

INDUSTRIAL APPLICABILITY

A painted article having a cured film formed by using a powder paint ofthe present invention is excellent in surface smoothness, has noabnormal appearance such as orange peel, and has high weatherresistance, anti-fouling property, etc., whereby it is useful for e.g.exterior building materials such as radio steel towers, power pylons,guardrails, automobiles, railway vehicles or aircrafts, traffic signalpoles, sign boards, etc.

What is claimed is:
 1. A powder paint, comprising: a fluororesin (A), atleast one metal element (B) selected from the group consisting ofpotassium, sodium and magnesium in an amount of from 2 to 60 mass ppmrelative to the fluororesin (A), a light stabilizer (C) in an amount offrom 10 to 10,000 mass ppm relative to the fluororesin (A), apolymerization inhibitor (D) in an amount of from 100 to 5,000 mass ppmrelative to the fluororesin (A), and free chlorine atoms with a massratio of the metal element (B) to the free chlorine atoms of from 1.0 to10.0.
 2. The powder paint according to claim 1, wherein the fluororesin(A) is at least one member selected from the group consisting of apolyvinylidene fluoride and a copolymer containing units based on afluoroolefin and units having a reactive group.
 3. The powder paintaccording to claim 1, wherein the fluororesin (A) is a fluororesinhaving a glass transition temperature of at least 30° C.
 4. The powderpaint according to claim 1, wherein the fluororesin (A) has a numberaverage molecular weight of from 3,000 to 50,000.
 5. The powder paintaccording to claim 1, wherein an amount of the free chlorine atomsranges from 0.1 to 30 mass ppm relative to the fluororesin (A).
 6. Thepowder paint according to claim 1, further comprising: a non-fluororesin(E) in an amount of from 10 to 400 parts by mass per 100 parts by massof the fluororesin (A).
 7. The powder paint according to claim 1,wherein the light stabilizer (C) is a hindered amine light stabilizerhaving a molecular weight of from 300 to 5,000 and a melting point offrom 50 to 250° C.
 8. The powder paint according to claim 1, wherein thepolymerization inhibitor (D) is a hydroquinone.
 9. The powder paintaccording to claim 6, wherein the non-fluororesin (E) is an acrylicresin or a polyester resin.
 10. A painted article, comprising: a curedfilm of the powder paint according to claim 1 on a substrate surface.11. The painted article according to claim 10, wherein the cured filmhas a thickness of from 100 to 1,000 μm.
 12. The painted articleaccording to claim 10, wherein the cured film has a water content angleof from 1 to 55°.